fix(dev-server): preserve nested component named slots

packages/dev-server/test/nested-named-slots.test.ts

@@ -0,0 +1,24 @@
+import { expect, test } from "bun:test";
+import { fillSlots } from "../src/runtime.ts";
+
+test("an outer default slot preserves a nested component's named slots", () => {
+  const child =
+    '<div data-component="LayoutSplitter"><div data-slot="start">Inbox</div><div data-slot="end">Message</div></div>';
+  const shell = fillSlots("<main><slot></slot></main>", child, true);
+  expect(shell).toContain(child);
+  const panes = fillSlots(
+    '<section><slot name="start"></slot><slot name="end"></slot></section>',
+    '<div data-slot="start">Inbox</div><div data-slot="end">Message</div>',
+    true,
+  );
+  expect(panes).toContain("Inbox</wrn-slot>");
+  expect(panes).toContain("Message</wrn-slot>");
+});
+
+test("void children do not swallow following direct named slots", () => {
+  const html = fillSlots(
+    '<slot name="header"></slot><slot></slot>',
+    'Text<input><div data-slot="header">Heading</div><p>Body</p>',
+  );
+  expect(html).toBe("HeadingText<input><p>Body</p>");
+});